Some statements may merely provide background information related to the present disclosure and may not constitute prior art.
Stimulation treatments, primarily hydraulic fracturing, are required in many types of formations, including shale gas reservoirs in order to obtain commercial production rates and to increase the area of reservoir that can be effectively drained with a wellbore. Wellbores are drilled in most of the gas shale reservoirs today as the standard completion practice as it has been shown that being able to contact more of the reservoir with the wellbore and then hydraulic fracturing along it results in the best rate/recovery/economics compared to vertical wells.
In hydraulic fracture stimulation operations for horizontal wellbores, one goal is to effectively stage alternate pumping sequences in order to get as near complete stimulation coverage as possible. For example, the simplest method of hydraulic fracturing the horizontal wellbore would be to not provide any attempt at isolation/diversion and simply bullhead the treatment fluid at a high rate, in some cases, with the hopes that some of the treatment will go to all parts of the reservoir. This has been shown to be very ineffective based on post-treatment evaluation of the production behavior along the wellbore. One of the most comprehensive approaches would be to isolate and hydraulically fracture stimulate at very small increments along the horizontal wellbore from the toe back to the heel. There are different approaches in between these extremes that may provide the best return on investment for different reservoir conditions.
One multi-stage fracturing technique involves the use of pump-down bridge plugs and perforating guns (see FIG. 1—Prior Art). In this type of multi-stage fracturing, the horizontal wellbore is divided into a number of sections (the number of sections depends on a number of factors such as wellbore length, geomechanical, petrophysical, etc. information on the shale in the horizontal section, shale zone thickness, etc.) to be hydraulically fracture stimulated. In order to make the pumping operations as efficient and less costly to the operator as possible, major time delays are minimized, and pumping is conducted as continuously as possible, but the ability to conduct the operation in this way can differ significantly for different shale reservoirs, clients, etc.
In some operations, for the first fracture stimulation stage of a horizontal wellbore, the perforation clusters are shot with perforating guns in the section nearest the toe of the horizontal wellbore. The hydraulic fracture stimulation is pumped into this section of clustered perforations as per the treatment design. At some point during a flush stage of the treatment, the inlet location of the fluid at the surface will be changed so a bridge plug and perforating gun combo (on wireline or slickline) can be pumped down the wellbore in order to isolate the previous fractured stage, to allow perforation of the next set of clustered perforations, so the next fracture stimulation stage can be performed. After the bridge plug is placed above the section that has just been fracture stimulated, a next set of clusters can be perforated and the perforating gun is extracted from the wellbore via wireline/slickline. The next fracture stimulation stage can be pumped and the process is repeated until the entire horizontal wellbore has been stimulated, as illustrated in FIG. 2—Prior Art. FIG. 2—Prior Art shows result after completion of the fracture stimulation for four sections of the horizontal wherein the perforation clusters for each section and the bridge plugs isolating each lower stage from the subsequent fracture stimulation treatment
Within each of these sections shown above in FIG. 2—Prior Art, the clusters of perforations may be shot in the best attempt to effectively stimulate the entire section. Depending on several variables, it may be optimum to provide a means of fluid diversion within the section being fracture stimulated in order to ensure adequate coverage of each of the perforation clusters.
In some cases, perforation clusters are phased perforations shot over a span of about 1 to about 2 ft of the casing in order to maximize opportunities to create separate non-interacting hydraulic fractures. Different techniques of trying to ensure coverage of all of the clustered perforation set includes, but is not limited to, limited entry perforating, use of particulate chemicals, use of perforation ball sealers, use of fiber diversion, as well as any other suitable techniques. The use of different types of diversion depends on wellbore conditions, risk mitigation, formation damage considerations, and the like. Another major consideration is whether or not the fracture stimulation treatment is being monitored in real-time with microseismic. With microseismic monitoring it is possible to infer the perforation clusters that are accepting fluid during the pumping, as well as determining whether diversion during the pumping stage is effective.
The Applicants have found a new way of achieving a reliable diversion technique.